1. Technical Field of the Invention
The present invention relates generally to a gas sensor which may be employed in measuring the concentration of a selected component of exhaust gasses emitted from automotive engines, and more particularly to an anti-corrosion structure of such a gas sensor.
2. Background Art
Japanese Patent First Publication No. 10-10082 discloses a gas sensor to be installed in an exhaust pipe of an internal combustion engine for automotive vehicles to measure the concentration of a given gas component of exhaust emissions. FIG. 8 shows such a type of a gas sensor 9.
The gas sensor 9 consists essentially of a sensor element (not shown) to measure the concentration of a gas (will also be referred to below as a measurement gas), a housing (not shown) in which the sensor element is retained, and an air cover assembly 94 joined to a base end of the housing.
The air cover assembly 94 is, as illustrated in FIGS. 8 and 9, made up of an inner cover 941 and an outer cover 942. The inner cover 941 is joined to the base end of the housing. The outer cover 942 surrounds a base end portion (i.e., an upper end portion, as viewed in the drawings) of the inner cover 941.
The inner cover 941 and the outer cover 942 have portions 943 crimped circumferentially thereof.
However, when air is introduced into the gas sensor 9 from air inlets 945 formed in a base end portion of the outer cover 942, water 7 may enter a clearance between the inner cover 941 and the outer cover 942 along a path, as indicated by a thick line W and accumulate, as clearly illustrated in FIG. 9, especially in a clearance 96 near the crimped portions 943, which will lead to the corrosion of an interface 8 between the inner cover 941 and the outer cover 942. Specifically, when the water 7 accumulates in the clearance 96, it results in a variation in concentration of oxygen between the clearance 96 and the interface 8 to facilitate or promote the transfer of metal ions from the inner and outer covers 941 and 942, thereby causing the interface 8 to be eroded.